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Lecture 16 Supernova Light Curves and Observations

Lecture 16 Supernova Light Curves and Observations. SN 1994D. Supernovae - Observed Characteristics. See also http://www.supernovae.net/snimages/ http://snfactory.lbl.gov/ http://rsd-www.nrl.navy.mil/7212/montes/sne.html (broke 2009?). Spectroscopic classification of supernovae.

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Lecture 16 Supernova Light Curves and Observations

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  1. Lecture 16 Supernova Light Curves and Observations

  2. SN 1994D

  3. Supernovae - Observed Characteristics See also http://www.supernovae.net/snimages/ http://snfactory.lbl.gov/ http://rsd-www.nrl.navy.mil/7212/montes/sne.html (broke 2009?)

  4. Spectroscopic classification of supernovae

  5. Properties: Type Ia supernovae • Classical SN Ia; no hydrogen; strong Si II ll6347, 6371 line • Maximum light spectrum dominated by P-Cygni features of Si II, S II, Ca II, O I, Fe II and Fe III • Nebular spectrum at late times dominated by Fe II, III, Co II, III • Found in all kinds of galaxies, elliptical to spiral, some (controversial) evidence for a mild association with spiral arms • Prototypes 1972E (Kirshner and Kwan 1974) and SN 1981B (Branch et al 1981) • Brighest kind of supernova, though briefer. Higher average velocities. Mbol ~ -19.3 • Assumed due to an old stellar population. Favored theoretical model is an accreting CO white dwarf that ignites at the Chandrasekhar mass.

  6. Spectra of SN Ia near maximum are very similar from event to event Spectra of three Type Ia supernovae near peak light – courtesy Alex Filippenko

  7. The Phillips Relation (post 1993) Broader = Brighter Can be used to compensate for the variation in observed SN Ia light curves to give a “calibrated standard candle”. Note that this makes the supernova luminosity at peak a function of a single parameter – e.g., the width.

  8. Possible Type Ia Supernovae in Our Galaxy SN D(kpc) mV 185 1.2+-0.2 -8+-2 1006 1.4+-0.3 -9+-1 1572 2.5+-0.5 -4.0+-0.3 1604 4.2+-0.8 -4.3+-0.3 Tycho Kepler Expected rate in the Milky Way Galaxy about 1 every 200 years, but dozens are found in other galaxies every year. About one SN Ia occurs per decade closer than 5 Mpc.

  9. Properties: Type Ib/c supernovae • Lack hydrogen, but also lack the Si II6355 feature that typifies SN Ia. • SN Ib have strong features due to He I at 5876, 6678, 7065 and 10830 A. SN Ic lack these helium features, at least the 5876 A line. Some people think there is a continuum of properties between SN Ib and Sn Ic • Found in spiral and irregular galaxies. Found in spiral arms and star forming regions. Not found in ellipticals. • Often strong radio sources • Fainter at peak than SN Ia by about 1.5 magnitudes. Otherwise similar light curve. • Only supernovae definitely associated with gamma-ray bursts so far are Type Ic

  10. Filippenko, (1996), Ann. Rev. Astron. Ap

  11. Properties: Type II supernovae • Have strong Balmer lines – H, H, H - in peak light and late time spectra. Also show lines of Fe II, Na I, Ca II, and, if the supernova is discovered early enough, He I. • Clearly come from massive stars. Found in star forming regions of spiral and irregular galaxies. Not found in ellipticals. Two presupernova stars identified: SN 1987A = B3 supergiant; SN 1993J = G8 supergiant (Aldering et al 1994) • Fainter than Type I and highly variable in brightness (presumably depending on hydrogen envelope mass and radius and the explosion energy). Typically lower speed than Type Ia. Last longer. • Come in at least two varieties (in addition to 87A) – Type II-p or “plateau” and Type II-L or “linear”. There may also be Type II-b supernovae which have only a trace amount of hydrogen left on what would otherwise have been a Type Ib/c (e.g., SN 1993J) • Strong radio sources and at least occasionally emit neutrino bursts

  12. Typical Type II-p on the Plateau Filippenko (1990)

  13. 2 days after SN) SN 1987A Philipps (1987) CTIO

  14. Summary

  15. and IIn’s

  16. As of SN 2000ek, 1791 supernovae had been discovered; the last supernova in 2004 was SN 2004io – SN number 249

  17. Supernova Frequencies Van den Bergh and Tammann, ARAA, 29, 363 (1991) Based upon 75 supernovae. 1 SNu == one supernova per century per 1010 solar luminosities for the host galaxy in the blue band. h ~ 0.7. The Milky Way is an Sb or Sbc galaxy. see also Tammann et al (1994) ApJS, 92, 487.

  18. Sharon et al. 2007, ApJ, 660, 1165

  19. MNRAS, 395, 1409 (2009) Volume limited sample

  20. MNRAS, 395, 1409 (2009) 10.5 year volume limited (28 Mpc) search for both SNe and their progenitors

  21. Van den Bergh and Tammann (1993) These numbers are probably high by a factor of about 2. Tammann et al (1994) says total SN rate in MW is one every 40+-10 years, with 85% from massive stars. The very largest spirals produce about 10 SNae per century. Good rule of thumb - 2 core collapse supernovae per centery; one SN Ia every other century

  22. Type II Supernovae Models and Physics of the Light Curve

  23. ~1045? Shock break out and cooling Typical Type II Plateau Supernova Light Curve 43 log luminosity plateau (recombination) 42 Radioactive Tail 0 few months time

  24. For a typical red supergiant derived from a star over 8 solar masses. • Break out – temperatures of 100’s of thousands K. Very brief stage, not observed so far (indirectly in 87A). Shock heating followed by expansion and cooling • Plateau – the hydrogen envelope expands and cools to ~5500 K. Radiation left by the shock is released. Nearly constant luminosity (T is constant and radius of photosphere does not change much – around 1015 cm). Lasts until the entire envelope recombines. • Radioactive tail – powered by the decay of radioactive 56Co produced in the explosion as 56Ni. The light curve will vary depending upon the mass of the envelope, radius of the presupernova star, energy of the explosion, degree of mixing, and mass of 56Ni produced.

  25. Shock Break-out • The electromagnetic display begins as the shock wave erupts • through the surface of the star. A brief, hard ultra-violet (or even soft • x-ray) transient ensues as a small amount of mass expands and cools very • rapidly. • The transient is brighter and longer for larger progenitors but hotter • for smaller ones

  26. Nadyozhin, Blinnikov, Woosley, in preparation T-color will be about twice T-eff, close to 5 x 105 K.

  27. For SN 1987A detailed calculations exist. It was little hotter because it was a BSG with 10 times smaller radius than a RSG. So far these transients have escaped detection, but the effects of break out in SN1987A were measured.

  28. The effect of the uv-transient in SN 1987A was observed in the circumstellar ionization that it caused. The first spectroscopic observations of SN 1987A, made 35 hours after core collapse (t = 0 defined by the neutrino burst) – Kirshner et al, ApJ, 320, 602, (1987), showed an emission temperature of 15,000 K that was already declining rapidly. Ultraviolet observations later (Fransson et al, ApJ, 336, 429 (1989) showed narrow emission lines of N III, N IV, N V, and C III (all in the 1200 – 2000 Angstrom band). The ionization threshold for these species is 30 to 80 keV. Modeling (Fransson and Lundquist ApJL, 341, L59, (1989)) implied an irradiating flux with Te = 4 to 8 x 105 K and an ionizing fluence (> 100 eV) ~ 2 x 1046 erg. This is in good agreement with the models. The emission came from a circumstellar shell around the supernova that was ejected prior to the explosion – hence the narrow lines.

  29. Fransson et al (1989) IUE Observations of circumstellar material in SN 1987 A

  30. x-ray UV 0.3 - 10 keV Soderberg et al 2008, Nature, 453, 469 Shock breakout in Type Ib supernova SN 2008D (serendipitous discovery while observing SN 2007uy)

  31. FUV = 1539 A NUV = 2316 A GALLEX discovery of ultraviolet emission just after shock break-out in a Type II-p supernova 2006bp (Gezari et al 2008, ApJ, 683, L131). Missed the initial peak (about 2000 s, 90 Angstroms) but captured the 2 day uv-plateau

  32. 2. Envelope Recombination Over the next few days the temperature falls to ~5500 K, at which point, for the densities near the photosphere, hydrogen recombines. The recombination does not occur all at once for the entire envelope, but rather as a wave that propagates inwards in mass – though initially outwards in radius. During this time Rphoto ~ 1015 – 1016 cm. The internal energy deposited by the shock is converted almost entirely to expansion kinetic energy. R has expanded by 100 or more (depending on the initial radius of the star) and the envelope has cooled dramatically. As a result only ~1049 erg (RSG; 1048 BSG) is available to be radiated away. The remainder has gone into kinetic energy, now ~1051 erg. As the hydrogen recombines, the free electron density decreases and kes similarly declines. (note analogy to the early universe)..

  33. Propagation of the Recombination Front: Since Te remains constant at about 5500 K, the recombination front moves inwards (in the co-moving frame) at an ever increasing rate. Since Tinterior decreases with time, the speed of the recombination wave accelerates

  34. How much mass recombines as a function of time? Woosley, ApJ, 330, 218 (1988) Where dM/dt is the rate at which matter flows through the photosphere and e is its internal energy. if L = const

  35. H ionization - 15 solar masses. When the recombination reaches the He core the plateau ends

  36. Photospheric speed Kasen and Woosley (2009)

  37. The luminosity of the supernova on the plateau is approximately proportional to the initial radius of the presupernova star. The shock deposits about half of its energy in the envelope of a blue or red supergiant, but the former must expand by an additional factor of 10 before it begins to recombine at 1015 cm. Since the internal energy e is proportional to 1/r, the star loses an additional factor of 10 in both luminosity and total radiate output. This is why SN 1987A was a comparatively faint supernova .

  38. Popov (1993, ApJ, 414, 712) gives the following scaling relations which he derives analytically: not quite linear in R because a more compact progenitor recombines at a slightly smaller radius. In fact the correct duration of the plateau cannot be determined in a calculation that ignores radioactive energy input.

  39. Cosmology on the Plateau Baade-Wesselink Method

  40. Eastman, Schmidt, and Kirshner (1996)

  41. Modeling the spectrum of a Type II supernova in the Hubble flow (5400 km/s) by Baron et al. (2003). SN 1993W at 28 days. The spectrum suggests low metallicity. Sedonna code.

  42. 3. Light Curve Tail Powered by Radioactive Decay

  43. 1238 keV 847 keV

  44. 1.2 B explosion of 15 solar mass RSG with different productions of 56Ni indicated by the labels. Kasen et al. (2009)

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